In the manufacture of ball valves, particularly bar stock valves wherein the housing is fabricated of a length of hollow bar stock, one common technique employed is to size the internal diameter of the housing at one end thereof so that it is sufficiently large to permit the ball and one or more seats to be inserted in sequence into the housing via said one end, whereafter the inserted elements are held in place by a hollow cylindrical end plug which is screwed into the housing opening through which the ball and seat were inserted. The end plug typically has an external thread which mesh engages an internal thread in the housing, and the end plug is screwed down into the housing sufficiently to hold the parts in assembled configuration.
A typical end plug which has been employed heretofore has an external flange of hexagonal or other configuration which can be grasped by an appropriate tool to screw the end plug into place during assembly of the valve. The interior diameter of the end plug is normally provided, moreover, with further threads which are adapted to thread engage a pipe with which the assembled ball valve is to be associated. If the end plug is not somehow locked to the ball valve housing after the end plug has been screwed into place, the possibility exists, e.g. when the ball valve assembly is unscrewed from an associated pipe line for service purposes or the like, that the end plug may be unscrewed from the ball valve housing along with the pipeline. This possibility poses serious risks in that, if there is fluid under pressure in the ball valve at the time the pipeline is being removed from the ball valve, the ball may fly out of the ball valve when the valve is removed from the pipeline along with the said end plug, or there may be a discharge of high pressure fluid from the interior of the ball valve which could cause possible injury to the operator, or the ball valve might simply fall apart.
To avoid these undesirable eventualities, it has been recognized heretofore that the end plug should preferably be locked to the ball valve housing after it has been screwed into place in the housing. One technique which has been suggested heretofore for this purpose is to weld the end plug into place after the ball valve is completely assembled. This technique cannot be employed, however, when the materials employed to fabricate the housing and end plug are, for example, brass, since brass is not weldable. Moreover, even when the elements being assembled are fabricated of steel, welding has the disadvantage that the parts cannot thereafter being readily disassembled to service the valve, and in addition, the welding operation tends to cause some splatter of the welding material which may contaminate the ball or seats. Further, considerable care must be taken to assure that the heat generated during the welding operation does not degrade the seat or parts of the valve adjacent the weld joint. The possibility of such degradation is, indeed, such a serious problem that it is impractical to use a brazing technique when the housing and end plug materials are formed of brass, stainless steel or carbon steel since brazing generates too much heat.
The locking of the end plug to the valve housing could be done by drilling one or more holes through the valve housing and into the end plug and then inserting a pin or pins into said holes. Such a pinning technique has a number of other disadvantages, however. It requires, for example, that the valve be machined after it has been assembled, and the the machining operation is one which necessarily produces chips which may end up inside of the valve and which could become embedded in the valve seat or score the ball. Also, unless a sufficient number of pins are employed, the pinning technique will not provide sufficient strength to keep the plug in place when the ball valve is unscrewed from a pipeline, but the provision of the comparatively large number of pins required to achieve adequate strength aggravates the chip problem. A pinning technique is moreover, time consuming and costly and, in addition, has the disadvantage that the end plug cannot be readily removed to service or repair the ball valve. Further, even where it is possible to remove the pins for service purposes, on subsequent reassembly of the valve it is highly unlikely that the previously machined holes will line up exactly, and therefore new holes may have to be drilled for the insertion of new pins at the time of reassembly, with a repetition of all of the problems mentioned.
The foregoing problems have been found, in practice, to be so difficult to solve that many valve manufacturers do not lock the end plug in place, and simply tolerate the risks which may be encountered in the use of an unlocked structure.
The present invention provides a novel valve housing structure which obviates all of the foregoing problems, which permits an end plug to be quickly and reliably locked in place when the valve is initially assembled, and permits the valve to be readily disassembled for repair or maintenance purposes and thereafter reassembled with the end plug again being quickly and reliably locked in place.